What Big Little Lies are the cast of the HBO drama covering up in season two?

We're not sure -- but it looks like Reese Witherspoon's Madeline Martha Mackenzie just uncovered another secret.

Witherspoon was snapped looking shocked with her mouth agape while filming a scene with Nicole Kidman and Meryl Streep on location in Monterey, California, on Thursday. Streep, meanwhile, couldn't have looked happier as she smiled from ear to ear while sitting opposite her new co-stars.

While Streep joined the cast in January, Witherspoon took to Instagram on Thursday to share a snap of another new co-star: a dog named Jolly! "Introducing Jolly. He has the best hair of all the cast !! #BigLittleLies @nicolekidman @hbo," she captioned the pic.

Kidman shared the first pic of Streep in character as Mary Louise Wright, the mother of the recently deceased Perry Wright (Alexander Skarsgard). Perry -- the abusive husband of Celeste (Kidman) -- died at the end of season one at the hands of Bonnie (Zoe Kravitz).